Hydraulic cushion for a press



Feb. 9, 1960 F. M. WILLIAMSON HYDRAULIC CUSHION FOR A PRESS Filed Jan. 23, 1959 United States "atent This invention relates to a press of the ram type em.- ploying a die pad which is adapted to engage the Work upon closing of the press, and has particular reference to a hydraulic cushion in the form of a hydraulically controlled piston for reacting against the die pad to resist movement thereof upon closing of the press and to return the die pad to-its extended position upon opening of the press.

The presence of air in the cylinders of a system of hydraulically controlled pressure pads is very objectionable and may cause improper functioning of the system. Since the air is compressible, while the oil that is used in such a system is not compressible, the presence of air in the hydraulic cylinders will require that the pistons, and consequently the die pads which react against the pistons, move through a substantial part of their travel before the air is sufliciently compressed to build up the required pressures in the cylinders. Furthermore, air within the cylinders may cause an undesirable spring backof the pads when the pressure is reduced upon the beginning of the return stroke of the press. This latter objection is particularly undesirable in a system of this type employing a time delay in the return of the die pads to their extended position. The present invention is directed to the provision of means for bleeding oii the airthat may be present in the hydraulic cylinders to overcome the above-mentioned difficulties in systems of this type.

.It is a principal object of the invention to provide a hydraulically controlled pressure pad system having means for bleeding air from the hydraulic cylinders employed in the system.

A further object of the invention is to provide a novel piston and cylinder construction for a hydraulically controlled pressure pad in a press.

Other and further objects of the invention will be apparent from the following description and claims and may be understood by reference to the accompanying drawing, which by way of illustration shows a preferred embodiment of the invention and what I now consider to be the best mode of applying the principles thereof. Other embodiments of the invention may be used without departing from the scope of the present invention as set forth in the appended claims.

' In the drawing:

Fig. l is a fragmentary perspective view with parts broken away of a ram type press having a hydraulically controlled pressure pad; and

Fig. 2 is a schematic view illustrating the hydraulic cylinders forming a part of the invention and the hydraulic control circuit for the cylinders.

In. Fig. 1 there is disclosed a portion of apress which.

2,924,446 Patented Feb. 9, 1960 ice Oil from the tank so is supplied to the cylinders 24 and 25 through a hydraulic pressure line 34 leading from the outlet 36 of a valve unit 38. The valve unit 38 includes a valve body having an inlet 40 to which the line 42 is connected for delivering oil from the tank-'30 to the valve 38. The valve is provided with a passage 44 communicating with the inlet 40 and with a passage 46 leading to a check valve 48 seated against the lower end of the passage 46 by a spring 50. A passage 52 leads from the lower end of passage 46 to the outlet 36. Oil under the predetermined relatively low pressure provided by the compressed air within the tank 30 is supplied to thecylinders 24 and 25 through the line 42, inlet 40, passages 44 and 46, past check valve 48, and through passage 52 and outlet 36 to the high pressure line 34.

The piston. 26 is provided with a downwardly opening recess 60, while the cylinder 24 has its inlet 62 disposed opposite the recess 60 in the piston 26. The cylinder 24 is provided with a hollow tube 64 extending from its inlet 62 upwardly into the lower end of the recess 60 in piston 26. An annular passage 65 is defined between tube 64 and piston 26. Piston 27 has a recess 66, opposite the inlet 62 to cylinder 25. A hollow tube 67 extends upwardly into recess 66 in spacedrelation.

upper end of the tube 64 and into cylinder 25 through the openings 71in tube 69. The oil under. the predetermined pressure maintained within the tank 30 will hold the pistons 26 and 27 and die pad 16 in their extended positions.

As the ram 10 of the press engages the work 28 the pistons 26 and 27 will resist downward movement of the die pad due to the hydraulic pressure within the cylinders 24 and 25. As the pistons move downwardly within their cylinders as the ram 10 is lowered, the oil within the'cylinders will be forced back through the line 34 and the line 72 into a passage 73 in the valve unit 38. Communication between passage 73 and passage 44 is normally closed by a pressure relief valve 74 which is held on its seat by a spring 76 confined between the relief valve 74 and a washer 78. An adjusting screw 80 is provided for adjusting the compression of spring 76 to provide an' adjustment of the pressure at which the valve 74 will open. A passage 82 communicates with passage 73 and intersects a valve bore 84 having a timedelay valve 86 therein. The valve 86 is provided with a reduced portion 88 so that oil returning from the cylinders through lines 34 and 72 and passages 73 and 82 will flow past the reduced portion 88 of the valve 86 into passages 90 and 92. Oil will flow from passage 92 into passage 94 and through passage 90 past check valve 95 into passage 94, from which the oil flows to passage '96 into the pocket 98 at the end of the valve bore 84 to react against the'right-hand end of the valve- 86. The

flow of oil into the right-hand end 98 of the valve bore 84 will force the ,valve 86 to the left against the force of spring 100 which is confined between the valve 86-and A supply tank 30 containing a,

and 27 will build up-the pressure in the lines 34 and 72 and passage 73 until the predetermined pressure at which the pressure relief valve 74 is set is attained, whereupon the valve 74 will open to return the oil to the supply tank 30 through the passage 44 and line-4 2.

' fAfter the ram 'has-cornpleted its working stroke and begins to raise, the pressure within thecylinders 24'and 25 'Wiil' b6 reduced so that the pressure-relieffvalve 74- will close. However, the valve 86 provides a time delay for the refilling of the cylinders since the 'passage-46 is 7 closed by. thethe valve 86 until the pressure withi'n the end 98 of the valve bore 84"is reduced sufliciently for the spring 100 to return the valve 86 to its righghand position. With the vale 86 inits left-handepositiori the portion 104 thereof closes off the -passage -9 2 so that the oil at the right-hand end of the-valve canl'only escape through passages 96 and- 94 past-a 'bleeder" valve 106 which restricts flow. through the passage 94L The valve 106 is provided with-an'adjustingscrew '108 to regulate the flowofoil through passage 94.

7 As soon as the valve 86 moves to its right-hand posinod, 'oil will again be-supplied to the cylinders '24 and 25 through passages 44 and 46 past check valve 48 and through the outlet 36 from the "valve body to theline'34.

The valve arrangement described provides a timefdelay for return of the'pad 16 to its extendedpositioii. w

in said by-pass passage set to open to return oil to the -The cylinders 24 and 25 are provided with means! for bleeding air therefrom and returning such air to the supply tank during the working strokeof the press.

The air bleed arrangement for the'cylinder24 comprises the tube 64. As the piston 26 moves downwardlywithin the cylinder 24, oil will be forced-at high velocitythrough the annular passage 65 and recess 60 anddeflected into tube'64. Any air in the cylinder will be forced'jwith the oil into the upper end of the tube64 and discharged therethrough as the piston 26 continues its downward movement. The air bleed arrangement forthe cylinder 25 "is similar in principle and operation to that described in connection with the 'cylinder'24. The air Within cylinder '25 will be forced ahead of the oil discharged from the cylinder through passage 68: and "will pass through the series of openings'71 at the upper end of tube 69 and through tubes 69 and 67 to line 34. It will be apparent that any air that might be present in: the cylinders? will be forced ahead of the oil into the line 34 'thepistons move downwardly with the working strokeofjflthe ram. The air will be forced ahead of the oil through the'lines 34-and 72 into the'passage 73 and past the pres,- s'ure'relief valve 74 when such valve is opened upon continued movement of the pistons 26 and 27. The air will in this manner be forced ahead of the oil back'to'fthe supply tank 30 where it will rise to the compressed air space above the level of the oil'in the tank'30,

Whilethe air bleed arrangements for the cylinders 24 and 25 have been illustratedlas being somewhat diiferent in construction, it will be apparent-that eitherof the' arrangements shown may be used; in cach of the cylinders.

The valve unit 38 disclosed herein forms 'the subj ect matter of my copending application Serial No. 703,667 filed December 18, 1957, nowUnitedSt'ates'Patent 'No. 2,901,238. r v s a While I have illustrated'and described a prefe embodiment of my invention, it is understood that this is capableof modification, andI therefore do not "to be limited to the precise detailsset forth but'des'ire to avail myself of suchchanges and alterations as fall:

its;; extended position .upon opening ofthe press, saidhydraulic cushion comprising a-work cylinder having a tank when the pressure in said cylinder is increased substantially above said predetermined pressure, said cylinder having a tube therein through which oil is supplied to and exhausted from said cylinder, said piston having a recess into which said tube is received upon movement of said piston into the cylinder, said piston and tube defining a restricted passage therebetween through which oil fiows into and out of said cylinder, said tube being arranged to bleed 0E air in said cylinder with vthe oil forced through said tube'by said'movement of said piston whereby suchair is returned with the oil to said supply tank through said pressure relief valve.

In a ram type press having a die pad engaged by the workupon closing. of the press, a hydraulic cushion forxsaidf die pad adapted to resist movement of the die padupon'closing of the press and to return the die pad to its extended position upon opening of the press, saidihydraulic cushioncomprising a work cylinder hav, ing a pistontherein reacting against said die pad, an oil a supply tank, means for maintaining the oil in said tank under a predetermined pressure, a hydraulic pressureline for supplying oil atsaid predetermined pressuretd said work cylinder, a check valve in said line past which oil is supplied to said cylinder, a bypass passage around bleeding off the pressure applied to said time-delayjv'alve to allow the same to be opened by said spring means after a predetermined time delay, thereby to allovt oil at said predetermined pressure to flow past saidcheck valve to said cylinder to return said die pad to its extended position, said cylinder having an axially extending tube therein connected to said hydraulic pressure line and through which oil is supplied to and exhausted. from said cylinder, said piston having a recess therein into .Which s-aid tube is received upon movement'of said piston into said cylinder, said piston and tube defining an annular passage therebetween for the flow of oil into and out of said cylinder, said tube being arranged to bleed off air in said cylinder with the oil forced through said tube by movement of saidpiston into saidcylinder. whereby such air is returned with the oil to: said supply,

tank through said pressure relief valve.

3. In a ram type presshaving a .die padiengaged by the work upon closing of the press, a hydraulic cushion for said die pad comprising a work cylinder having a piston therein reacting against said die pad, anoil supply tank, a hydraulic pressure line for supplying oil fromj'sa'id tank to said work cylinder to move said piston toit's extended position and through which oil is returned to said supply tank upon closing of the press, said cylinder having an axially extending tube therein connected. to saidhydraulic pressure line and throughwhich' oil is supplied to andexhausted from said cylinder, said piston having a recess therein into which said :tube is received upon movement of said piston into said cylinder, said piston and tube defining an annular passage,therebetweenfor the flow of oil into and out'of said cylinder,

5 said tube having an opening therein within said recess to bleed off the air in said cylinder with the oil forced through said opening into said tube whereby such air is returned with the oil to said supply tank through said I hydraulic pressure line.

Y 4. In a ram type press having a die pad engaged by the work upon closing of the press, a hydraulic cushion for said die pad adapted to resist movement of the die pad upon closing of the press and to return the die pad to its extended position upon opening of the press, said hydraulic cushion comprising a work cylinder having a piston thereinreacting against said die pad, an oil supply tank, means for maintaining the oil in said tank under a predetermined pressure, a hydraulic pressure line for supplying oil at said predetermined pressure to said work cylinder, a check valve in said line past which oil is supplied to said cylinder, a bypass passage around said check valve and through which oil is returned from said cylinder to said supply tank, a pressure relief valve in said by-pass passage set to open to return oil to the tank when the pressure in said cylinder is increased substantially above said predetermined pressure, said cylinder having an axially extending tube therein through which oil is supplied to and exhausted from said cylinder, said piston having a recess therein into which said tube is received upon movement of said piston into said cylinder, said piston and tube defining a restricted passage therebetween for the flow of oil into and out of said cylinder, and an air bleed tube secured to said piston and arranged within the recess in said piston, said air bleed tube being telescopically related to the tube in saidcylinder and having an opening therein within said recess to bleed off the airin said cylinder with the oil forced through said opening into said tube upon movement of said piston into said cylinder whereby such air is returned with the oil to said supply tank through said pressure relief valve.

5. In a ram type press having a die pad engaged by the work upon closing of the press, a hydraulic cushion for said die pad adapted to resist movement of the die pad upon closing of the press and to return the die pad to its extended position upon opening of the press, said hydraulic cushion comprising a work cylinder having a piston therein reacting against said die pad, an oil supply tank, a hydraulic pressure line for supplying oil to said work cylinder to hold said piston in its extended position and through which oil is returned to said supply tank upon closing of the press, said cylinder having an axially extending tube therein through which oil is supplied to and exhausted from said cylinder, said piston having a recess therein into which said tube is received upon movement of said piston into said cylinder, said piston and tube defining an annular passage therebetween for the flow of oil into and out of said cylinder, and an air bleed tube secured to said piston and arranged within the recess in said piston, said air bleed tube being telescopically related to the tube in said cylinder and having an opening therein within said recess to bleed olf the air in said cylinder with the oil forced through said opening into said tube whereby such air is returned with the oil to said supply tank through said hydraulic pressure line.

6. In a ram type press having a die pad engaged by the work upon closing of the press, a hydraulic cushion for said die pad adapted to resist movement of the die pad upon closing of the press and to return the die pad to its extended position upon opening of the press, said hydraulic cushion comprising a work cylinder having a piston therein reacting against said die pad, said piston having an oil supply and exhaust port therein communicating with said cylinder, an oil supply tank, means for maintaining the oil in said tank under a predetermined pressure, a hydraulic pressure line connected to said port for supplying oil at said predetermined pressure to said work cylinder, a check valve in said line past which oil is supplied to said cylinder, a bypass passage around said check valve and through which oil is returned from said cylinder to said supply tank, a pressure relief valve in said by-pass passage set to open to return oil to the tank when the pressure in said cylinder is increased substantially above said predetermined pressure, said cylinder having a port therein communicating with said by-pass passage through which oil is exhausted from said cylinder, and means cooperable with said port in said piston upon movement of said piston into said cylinder for entraining air in the oil as it is expelled from said cylinder through said port so as to bleed 01f air from said cylinder upon each stroke of the press.

References Cited in the file of this patent UNITED STATES PATENTS 933,010 Wilzin Aug. 31, 1909 1,787,996 Rode Jan. 6, 1931 1,848,383 Rode Mar. 8, 1932 2,300,162 Maude Oct. 27, 1942 2,842,357 Williamson July 8, 1958 

